plain and simple, "smobilizzare" is the snobbish version of "vendere"

smobilizzare means to turn in to cash. As these are deposits held with banks then the only way to turn them into cash is to withdraw them. So in this context withdraw is the only translation possible that I can see. Clearly at some time in the next 12 months, once smobilizzato or withdrawn then the collateral will no longer exist. In over context smobilizzare is to disinvest, to sell to dispose of, but you can't sell a bank deposit.

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Note added at 18 mins (2020-07-21 19:52:56 GMT)
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Correction, "In other contexts smobilizzare is to...

I don't see how a deposit can be sold. Who buys it?

That it not be withheld by the bank

Italian term (edited): smobilizzare /depositi/

Looks more journalistic than legal, whilst straddles financial jargon.

recall an order and call in a loan, rather than deposits.